Fire-resistant pulpboard and method of making the same



TPateated May 9, 1933 No Drawing. 7

UNITED STATES PATENT OFFICE HUBER/1 L. BECKER, OF TRENTON, NEW JERSEY,ASSIGNOR TO THE AGASOTE m BOARD COMPANY, OF FERNWOOD ROAD, EWINGTOWNSHIP, MERCER COUNTY, NEW V JERSEY, A CORPORATION OF NEW JERSEYFIRE-RESISTANT PULPBOARD AND METHOD)! MAKHWG THE SAME My inventionrelates to a pulp board which is highly fire-resistant and to the methodof making the same.

My invention is of particular advantage in the manufacture of moldedpulp board, such as is usually made by running wood pulp, paper pulp orthe like into a mold and by means of pressure removing the majority ofthe water (see, for instance, United States Letters Patent No. 971,936dated 0ctober 4, 1910, and No. 1,272,566dated July 16, 1918) andsubsequently drying out the remainder of the water by the application ofheat. After it has been dried, or simultaneously with the drying, theboard may, if desired, be subjected to high pressure in order to compactthe same thus giving it higher tensile and transverse strength and ahigher degree of hardness. The object of my invention is to produce apulp board whose fibres are coated with aluminum hydrate to such anextent that the board is highly fireresistant and will smolder as littleas possfble, if at all, after having been exposed to flame.

It is a further object of my invention to apply aluminum hydrate tofibres in such a manner that when such fibres are molded or otherwiseformed into the preliminary shape of the finished board there will be aslittle interference as possible with the drainage of the water from thepulp and no undue warping of the wet board.

Other objects of my invention will be apparent from the followingdescription thereof.

In order to produce my fire-resistant pulp board in the best mannerknown'to me, I deposit upon the pulp fibres, before they are shaped intothe form of aboard, aluminum hydrate and calcium sulfate obtainedpreferably as precipitates from the double decomposition of aluminumsulfate and calcium hydrate. In the preferred form of my invention Ideposit upon the fibres also a suitable quantity of a colloidal clayknown as bentonite. The aluminum hydrate when obta ned as a precipitatefrom the double decomposition referred to is in a fine state ofsubdivision, and the calcium sulfate is Application filed June 24, 1981.Serial No. 546,665.

in very fine crystalline form. The bentonite, which is inferior toaluminum hydrate asa fireproofing agent, appears to assist the aluminumhydrate in coating the fibres more effectively and thereby aids it tocheck smol dering of the board after the latter has been exposed to aflame. The calcium sulfate,-

while not so valuable per se as the aluminum hydrate from the standpointof fireproofing,

increases the fire-resistant qualities of the board becausepresentinlarg'e quantities, and appears to perform a very valuablefunction in breaking up the continuity of the gelatinous depositpfaluminum hydrate, or aluminum hydrate and bentonite, on the fibres, .andfor this reason or for the reason that it acts as a spacing means tokeep the fibres slightly separated, aids, in permitting the water todrain from the pulp. Some of the calcium sulfate is, however, lost,being washed out in solution with the drainage wa ter, but the lossofcalcium sulfate in subsequent operations is diminished and eventuallyceases, if the drainage water holding calcium sulfate in solution isre-used in subsequent operations.

I prefer to cause the reaction between the aluminum sulfate and thecalcium hydrate to take place in the heater in whichfand while, the pulpis being beaten, first adding the aluminum sulfate and, when this hasbeen thoroughly dissolved in the beater, adding a suspension of'calciumhydrate, but I ma cause-such reaction, and obtain the precipitatesresulting therefrom, in a separate vessel, but then the precipitateshould be used as soon as possible to prevent agglomeration thereof. Thebentonite will have to be sus pended in water, but as this is a somewhatdifficult operation due to the finely divided nature of this material,I'prefer to mix the bentonite with the calcium hydrate before malt-- ingup the suspension of the former, thus eliminating one mixing operationand also reducing the viscosity of the bentonitesuspension by thepresence of the calciumhydrate.

The proportion of aluminum hydrate is preferably'such as will result inas'coinplete a fireproofing of the finished board 95 1 I so sibleWithout interfering with the proper felting of the fibres. Theproportion of calcium sulfate used is, for obvious reasons, convenientlysuch as would result from the double decomposition, when producingthereby the requisite amount of aluminum hydrate, but in any eventshould be just about sufficient to permit suitable drainage of the waterfrom the pulp without being used in such quantities as will interferewith giving the maximum lire-resistant qualities to the finished board,or with a proper felting of the fibres. As hereinafter explained, theproportion of calcium sulfate may under some circumstances be reducedwith advantage to the finished product. The proportion of bentonite tobe used in such as will, together with the aluminum hydrate used, coatthe fibres sufficiently to check smoldering as far as reasonablypossible. The exact proportions of these various substances will dependlargely upon the nature of the fibres to be used and the degree to whichthe resulting board is to be compacted but can, in any event, readily beascertained by simple experiment, enough being used to effect thedesired object, any more than this being more surplusage or interferingwith ease of manufacture of the board.

I prefer to render the board waterproof as well as fire-resistant andtherefore to add to the beaten mixture of the ingredients hereinabovereferred to the usual soap (sizing) and then to precipitate it onto thefibres.

My preferred method '(which results in the least costly board) thereforeincludes the following steps:

1. Preparation of a pulp suspension from any suitable fibre, such asWood fibre, chemically digested fibre, or mixtures thereof, as can beobtained, for instance, by beating up old newspapers; bagasse or strawmay be used.

2. Preparation of aluminum hydrate in the requisite finely divided form,and calcium sulfate, by adding aluminum sulfate to the beater, and whenthis is dissolved, adding a suspension of calcium hydrate in whichlatter the desired quantity of bentonite is also suspended. It isadvisable that the suspension of calcium hydratebe added graduallyto-the solution of aluminum sulfate and that enough he added to leavethe mixture slightly alkaline at the end.

. 3. The pulp suspension and the precipitates, together with thebentonite, are mixed in the beaten. If the pulp is to be subsequentlysized care should be taken to keep .or render the mixture neutral orslightly alkaline so as to avoid precipitation of the soap. 4. Asuitable rosin or other soap in weight equal to 4%-5% of the totalweight of fibre,

bentonite, aluminum hydrate and calcium sulfate, is added to the beatercharge as a sizing ingredient, preferably after the fireproofing agentshave been thoroughly mixed with the fibres.

5. The soap is then precipitated by adding a suitable quantity of asuitable precipitant, such as aluminum sulfate.

6. The pulp is then shaped in a mold or otherwise, and dried, or driedand compacted.

The resulting board is sufiiciently fire-re-.

sistant to comply with the majority, if not all, of the building codesof American cities; incidentally. the product, if waterproofed as abovedescribed, is water-resistant so as to permit its use in constructionwork exposed to the elements; it has rigidity and good mechanicalstrength with freedom from brittleness and a low heat transmission ascompared with hoards composed of mineral products, such as cement,asbestos or plaster.

The following examples will illustrate the proportions which may be usedin the manufacture of my board:

52.2% fibre 13.1% aluminum hydrate 29.5% calcium sulfate 5.2% bentonites Ewample2 3 Same as Example 1 using r Pounds Bentonite 300 thus givinga board of the composition 47.4% fibre 11.8% aluminum hydrate26.6%calcium sulfate [14.2% bentonite My invention may withsubstantially equalin my claims I refer to bentonite I intend to includeas an equivalent any clay of such a-degree of fineness, for instanceground china clay (kaolin) as will enable it to check smoldering to asubstantially valuable degree.

The above examples give one illustration of a change in proportion madedesirableby a change in the fibres used. In Example 1 the fibres usedwere obtained by grinding old newspapers and were fairly well hydratedand therefore tended tocling close together and thus prevent drainage,In Example 2, the fibres used were obtained from ground wood screeningsand therefore constituted a free draining stock and were thereforecapable of being made into a fire-resistant board with the use of a muchhigher proportion of bentonite. Instead of producing aluminum hydrate bythe double decomposition process with aluminum sulfate and calciumhydrate at the place of use, I may purchase aluminum hydrate of therequired state of subdivision and calcium sulfate crystals and mix them,but these materials if purchased separately are very much more costlythan if produced in the manner described, at or near the place of use.

The aluminum hydrate should preferably be of a degree of finenesssubstantially equal to that obtained from the double decompositionhereinabove described- It is to substantially this degree of finenessthat I refer when I speak in my claims of aluminum hydrate of the degreeof fineness described; If the parholes of aluminum hydrate are of a muchless degree of fineness a commercially valuable degree of vfirepro'ofingis not obtained, and if they are of a much higher degree'of fineness thedrainage of water from the wet pulp is so slow as to make the processcommercially impracticable. In place of the calcium element or thesulphur element, or both, I may substitute in whole or in part anelement or elements which when used with the aluminum element and thehydroxide radical give me aluminum hydrate in the fine state ofsubdivision described, and a crystal insoluble or difliculty soluble-inwater which can perform the function'ofthe calcium sulfate crystals,

, As a matter of fact under certain circumstances I prefer to substitutefor some of the calcium an element which will not cause the formation ofcrystals, so as to reduce the pro portion of crystals to the aluminumhydrate.

As long as a sufficient proportion of or stals IS su stantially the fullvalue of the presence of the crystals is obtained. The presence ofcrystals in excess of such proportion interferesto a certain extent withthe felting of the fibres and thus results in a boardof less hardnessthan could be producedif no such excess of crystals were present.AsaIready indicated the proportion of crystals necessary to permitreasonably free'drainage; depends upon" or ammonium sulfate" passing outwith the present to permit reasonably free drainage,-

the nature of; the fibre. For instance, ground wood screenings,untreated, form a free-flowing stock which does not call for thepresence of so high a proportion of crystals as does old newspaper stockwhich under ordinary circumstances permits only a very slow drainage.The following example will illustrate a modification of my process whichhas for its object the lowering of the proportion of crystals:

Ewample 3 Pounds This gives a board of the composition 50.3% fibre 12.5%aluminum hydrate 12.0% calcium sulfate 25.2% bentonite.

In the above example the fibre used is about two-thirds newspaper stockand one-third ground wood screenings, constituting therei fore, becauseof the presence of the screenings, a stock which is freer flowing thannewspaper stock alone. The proportion of slaked lime used is one-half ofthat used in Example 1 and there is substituted for the remainder of theslaked limeof Example 1, 98 lbs. of

ma nesium oxide. The resulting magnesium sul ate does not form crystalsbut. goes into solution in the drainage water and is'removed therewithsimultaneouslywith about 100 lbs. of the calcium sulfate as in Example1'. As a result the amount of calcium sulfate crystals' in the board(232 lbs.) is 'far-less than one-half of the amount of calcium sulfatecrystals (564: lbs.) of Example 1. Th1s.per-

mits ,a more complete felting of the fibres" and therefore a harderboard having a surface less liable .to be injured by abrasionthan thesurface of the product. of Example 1. This permits also the addition ofamuch higher proportion of .bentonite than in Example 1,, thus increasing.the insurance against smoldering. The presence of the bentonite even inthis high proportion does not interfere, at least to any substantialextent,

with thefree felting of the fibres, nor does it interfere withthedrainage of the stock. The addition of this high proportion of bentonitein Example 1 would increase unduly the proportion of mineral matter tofibre.

In Example 3, the magnesium oxide'may be replaced by caustic soda,sodium carbonate or ammonium hydrate, the resulting sodium 4 surface isobtained by dimmishing the proportion of crystals in the mannerindicated in Example 3. If a board having a harder surface is desiredand particularly one which will permitthe smoothing of such surface,

for instance, by sanding, a metallic soap of a drying oil (f. i.linseed, China. oil or perilla) is added to the furnish as the sizingngredi ent (Step4 and the board,after it has been dried, is be ed for aperiod of time, and at a temperature, sufficiently high to oxidize theoil. Of course. any suitable fillers or coating compositions (f. i.ethyl silicate) may be used which will improve the board withoutinterfering-with its fire-resistant qualities.

Board hardened by the use of a metallic soap of a drying oil may bedried to bonedryness before baking and in fact slrould be so dried. Onthe other hand, it is-of very great importance that a board notcontaining such a soa should not be dried to bone-dryness, but s ouldprefe' rabl have left within it-as high as 2% by weig t of moisture, asotherwise the fire-resistant qualities of the board are diminished toavery large extent.

- I am unable at this timeTto explain this henomenon but believe thatthe removal 0 the final fraction of moisture results in chemical changeswhich destroy in part the protection afforded by the aluminum hydrateand the bentonite.

. The proportion ofcrystals which under given circumstances may permitthe. frees t drainage of the water from the pulp after the board hasbeen shaped may, at least m some cases, be higher than desirable topermit the des'red extent of felting, i. 0., to produce the hardestpossible board. Therefore if a relatively soft and'highly porous boardis 'the desired product, it will be profitaia-Ie to use acomparatively'large proportion of crystals so as to permit speed ofoperation result in in xjeduced cost of production.- If a comparativelyhard board is the desired product,

: andthereforea smaller proportion of crystals must befused, speed ofproduction must be sacrificed. -The exact proportion of crystals niaytherefore have to be t e result of a: compromise in which somehardnessof product is sacrificed in" favor of speed of production, orvice versa. v

. I may substitute for some of the fibre, preferably about 20 percent,ground or granulated cork. .Such cork may be incorporated either in .itsnatural state or impregnated with suitable fireproofing agents such assulfate of ammonium, sodium molybdate, or boric acid,

preferably to such an extent that the weight of the salt is about 20percent of the weight of the fireproof cork. It may sometimes be with asuitable coating, for instance, calcium carbonate, to prevent escape ofthe water soluble salts. r v

The aluminum hydrate referred to by me is Al(OH),. Y

I claim:

1. A highly fire-resistant pulp board whose i individual fibres arecoated with aluminum hydrate and bentonite.

2. The method of making fireresistant pulp board which comprises mixingfibres, water in an amount sufficient to float them, aluminum hydrate ofthe degree of fineness described in an amount substantially sufficientto coat them and calcium sulfate crystals in an amount suflicient to.permit substantially free drainage of the water, shaping the resultingmixture into the form of a board, permitting the majority of the waterto drain away and then drying the mixture.

3. In the process of claim 2, the step of producing thealuminum h drateand the calcium sulfate crystals byd ouble decomposition of aluminumsulfate and calcium hydra e.

4. A highly fire-resistant pulp board whose individua fibres are coatedwith aluminum hydrate, bentonite and an oxidized drying o1 5. The methodof making fire-resistant pulp board which com rises mixing fibres, waterin an amount sui cient to float them, aluminum hydrate of the degree offineness described in an amount substantiallvsuili cient to coat themandcrystals substantially insoluble in water in an amountsuflicientto.

the majority of the water tals by double decomposition of an aluminumsalt and of a hydrate which will react to form aluminum'hydrate and acrystal substantially insoluble in water.

8. In'the process of claim 5, the step of producin some of the aluminumhydrate and all 0 the crystals which are substantially insoluble inwater by double decomposition of an aluminum salt and a suitablehydratev and the remainder of the aluminum hydrate by doubledecomposition of an aluminum salt and of a hydrate which will react toform aluminum hydrate and a substance soluble in water.

9. In the process of claim 5, the step 01 I producing some of thealuminum hydrate and all of the crystals by double decomposition ofaluminum sulfate and calcium hydrate and the remainder of the aluminumhydrate by double decomposition of aluminum sulfate and magnesiumhydrate.

10. In the method of making fire-resistant pul board claimed in claim 5,the step of ad mg to the mixture a metallic soap of a drying oil.

HUBERT L. BECHER.

